Secure OpenLDAP Autentication for a Small Network

Introduction and Concepts

This guide is composed from bits and pieces of LDAP guides and forums around the net. I borrowed very heavily from Eliott's (cactus) OpenLDAP guide [Ldap Server Setup] which is very well written. Unfortunately Arch Linux has some differences in the way things are setup. It is also the case that most LDAP guides online fall into one of 3 categories: too general, outdated or uses distro specific tools (i.e. authconfig). This guide is written specifically with Arch linux in mind and will try to illustrate both LDAP concepts and implementaion from the point of view of someone who has never used LDAP before (i.e. the author).

Configure TLS Encryption

It's a good idea to configure TLS to encrypt the exchange of information between client and server. This way passwords, which are normally sent plain-text, cannot be easily sniffed from the wire. In order to use TLS, we must first create a certificate. You can have a certificate signed, or create your own Certificate Authority (CA), but for our purposed, a self-signed certificate will suffice. IMPORTANT: OpenLDAP cannot use a certificate that has a password associated to it.

You will be prompted for information about your ldap server. Much of the information can be left blank. The most important information is the common name. This must be set to the DNS name of your ldap server. If your LDAP server's IP address resolves to example.org but its server certificate shows a CN of bad.example.org, LDAP clients will reject the certificate and will be unable to negotiate TLS connections (apparently the results are wholly unpredictable).

Now that the certificate files have been created copy them to /etc/openldap/ssl/ (if this directory doesn't exist create it) and secure them. IMPORTANT: slapdcert.pem must be world readable because it contains the public key.

The TLSCipherSuite specifies a list of OpenSSL ciphers from which slapd will choose when negotiating TLS connections, in decreasing order of preference. In addition to those specific ciphers, you can use any of the wildcards supported by OpenSSL. NOTE: HIGH, MEDIUM, and +SSLv2 are all wildcards.

To see which ciphers are supported by your local OpenSSL installation, type the following:

openssl ciphers -v ALL

In order to tell OpenLDAP to start using encryption edit /etc/rc.d/slapd and change

This will cause OpenLDAP to accept encrypted. IMPORTANT: If you created a self-signed certificate above be sure to add the following line to /etc/openldap/ldap.conf or you won't be able connect to the server to test it: